Detection material for ionizing radiation

ABSTRACT

A detection material for ionizing radiation. The material is solid at room temperature but meltable to a fluid at a temperature of about 100° C. One essential component in said detection material is a low molecular weight aromatic polymer, preferably a thermoplastic resin that contains low molecular weight polymer molecules of styrene and/or styrene derivatives. The detection material optionally contains a hot melt polymer and a wax-like substance, such as paraffin.

The object of the invention is a detection material for ionizingradiation, having at least one organic and/or inorganic scintillatingcompound and primarily intended for detecting radioactive samples thatreside on a support material. The detection material is intended fordetecting ionizing radiation in an arrangement where radioactive samplessituate on a measurement support, such as a filter plate or alike, andinto which detection material, such as scintillator, is added before themeasurement.

The invention relates in the first place to liquid scintillationcounting from a filter plate. A liquid scintillation counter of thistype is e.g. that manufactured by the applicant Wallac Oy with the tradename 1205 Betaplate. With this instrument, samples labeled withradioactive markers are measured that situate on a filter plate or onother corresponding plate. The size of the filter plate used by theapplicant is 10 cm×25 cm. On the plate samples are positioned in 16 rowsso that there are 6 samples in each row. The total number of samples onthe plate is 96. Every sample situates on an area with the diameter of 9mm.

According to a known method, the filter plate on which the samples to beinvestigated situate, is put into a flat plastic bag for themeasurement, and about 10 ml of liquid scintillator is added. The bag issealed e.g. with a heat sealer and is placed in a measuring cassette of1205 Betaplate liquid scintillation counter. The liquid scintillatorconverts part of the radiation energy emitted by the samples into lightthat is measured with the photomultiplier tubes of the scintillationcounter.

A drawback of this known method has been that in some cases the sampleson the filter plate have been noticed to gradually dissolve into saidliquid scintillator. If the samples then get mixed with each other,serious errors are introduced in the measurement.

The object of the present invention is to create a new detectionmaterial that is solid at room temperature and e.g. plate-shaped, butcan be melted to fluid by heating it to a temperature of about +100 Cwhereby the material penetrates into the filter plate. The measurementis performed after the detection material has cooled and solidified.

The detection material according to the invention is characterized inthat said detection material is solid at room temperature, but forbringing said detection material into intimate contact with said supportmaterial and radioactivity thereon, said detection material isoptionally meltable to fluid by heating. One essential component in saiddetection material is a low molecular weight aromatic polymer,preferably a thermoplastic resin that contains low molecular weightpolymer molecules of styrene and/or styrene derivatives.

The meltable detection material plate, or scintillator plate, accordingto the invention, removes the problem described above, because thesamples do not dissolve into the solid scintillator plate.

The other characteristics of the invention are presented in the patentclaims below.

In the following, detection material according to the invention and itsuse are described with the disclosed drawings where

FIG. 1 presents the detection material plate and the filter plate onwhich the sample has been positioned.

FIG. 2 presents the plates of FIG. 1 laid on each other.

FIG. 3 presents the filter plate of FIG. 2 into which the detectionmaterial plate has been melted.

The scintillator plate made of the detection material according to theinvention is used e.g. in the following way:

The filter plate 1, on which the samples 2 to be investigated situate,is put into a flat plastic bag into which also the solid scintillatorplate 3 is added that is of the same size as the filter plate. Thethickness of the scintillator plate is e.g. 0.2-2 mm. After this, thesolid scintillator plate 3 is melted into the porous filter plate 1 withe.g. a hot metal plate. During the melting period the liquid formed bythe material of the scintillator plate penetrates so near the radiationemitting sample molecules that the radiation and the material of thescintillator plate can interact.

After melting, the system is cooled down to room temperature where thematerial of the scintillator plate is solid again and the samples cannot, therefore, dissolve into it. As a result of interaction processes,part of the radiation energy emitted by the radioactive molecules isconverted to light that is measured with the mentioned liquidscintillation counter.

According to the invention, it has been found that suitable to one veryuseful component in the meltable detection material is a thermoplasticresin that contains low molecular weight polymer molecules of styreneand/or styrene derivatives.

The mentioned styrene derivatives are e.g. α-methylstyrene,vinyltoluene, dimethylstyrene, dimethyl-α-methylstyrene and tertiarybutylstyrene. Trade names of such resins are e.g. Piccotex, Kristalexand Nevbrite.

Low molecular weights of the mentioned resins are essential formeltability. Previously known in the art are high molecular weightpolystyrene and polyvinyltoluene that have been employed as basepolymers in so called plastic scintillators. However, these are noteasily meltable to fluid.

Furthermore, it has been found that suitable to second useful componentin the detection material is a polymer for hot melt adhesives (hot meltpolymer) that gives elasticity for the material at room temperature.Constitutional units of hot melt polymers are e.g. ethylenevinylacetate(EvA), ethylene-ethylacrylate (EEA) and ethylenebutylacrylate (EBA).

As a third component in the detection material, the actual scintillatingcompounds are used that are previously known in the art. Organicscintillating compounds are e.g. diphenyloxazole (PPO),phenylbiphenylyloxadiazole (PBD), bis(phenyloxazolyl)benzene (POPOP) andbis(methylstyryl)benzene (bis-MSB). The usefulness of the abovementioned resins, inventors assume, arises from the fact that theycontain aromatic groups that can transfer the excited states generatedby radiation to the mentioned organic scintillating compounds. Forspecial applications, inorganic scintillating compounds can also beadopted that are e.g. zincsulphide and yttriumsilicates activated withappropriate impurity atoms.

As an additional component in the detection material, paraffin oranother appropriate wax can be included to adjust the fluidity of themolten material.

Expressed as percentages by weight, the amounts of the mentionedcomponents are 10-99.5% of the low molecular weight aromatic polymer;0-60% of the hot melt polymer and 0-80% of the wax-like component. Theamounts of the components of an illustrative composition can be e.g. asfollows: resin 60%, hot melt polymer 10%, scintillating compounds 5% andparaffin 25%. Naturally, the amounts can be varied, if needed.

A homogeneous mixture is obtained from the mentioned components byheating them to sufficiently high temperature, e.g. +100 C, and mixingthem together. Of this mixture, scintillator plates with desiredthicknesses and to be used as described above.

The invention can also be used in some other applications, such as inautoradiography, where, with the invention, the energy of the radiationcan be converted to light that is allowed to expose photographic plateor film.

The invention is not confined to the presentation above, but it includesall meltable scintillator plates and bodies of other shapes that have asone component a thermoplastic resin that contains low molecular weightpolymer molecules of styrene and/or styrene derivatives.

We claim:
 1. A radioactive test plate comprisinga measurement support,at least one radioactive sample disposed on the measurement support, anda detection material in contact with the measurement support andradioactive sample, the detection material comprising at least onescintillation compound and an aromatic, thermoplastic polymer that is asolid at room temperature and meltable at a temperature of about 100° C.or higher to form a liquid.
 2. A radioactive test plate as define dinclaim 1, wherein the aromatic, thermoplastic polymer is a polymer of atleast one of styrene and a styrene derivative.
 3. A radioactive testplate as defined in claim 2, wherein the styrene derivative is a memberof the group consisting of α-methyl-styrene, vinyl toluene,dimethylstyrene, dimethyl-α-methylstyrene, and t-butylstyrene.
 4. Aradioactive test plate as defined in claim 1 wherein the detectionmaterial further comprises a hot melt polymer.
 5. A radioactive testplate as defined in claim 4, wherein the hot melt polymer is a member ofthe group consisting of polymers of ethylene vinylacetate, ethyleneethylacrylate, and ethylene butylacrylate.
 6. A radioactive test plateas defined in claim 1, wherein the detection material comprises 10-99.5per cent by weight of the aromatic, thermoplastic polymer, 0-60 per centby weight of a hot melt polymer and 0-80 per cent by weight of a wax. 7.A radioactive test plate as defined in claim 6, wherein the wax isparaffin.
 8. A method of preparing radioactive samples for testingcomprisingdisposing at least one radioactive sample on a measurementsupport, disposing a detection material on the measurement support, thedetection material comprising at least one scintillation compound and anaromatic, thermoplastic polymer, that is a solid at room temperature andmeltable at a temperature of about 100° C. or higher to form a liquid,heating the detection material to form a liquid which permeates themeasurement support and contacts the radioactive sample, and cooling thedetection material and the measurement support.